This invention relates to extruded cellular thermoplastic polymer foam materials useful for sound absorption applications.
Polymer foams having desirable sound absorption properties are well known. Many are also known that are made of thermoplastic materials. However, one of the drawbacks in using thermoplastic polyolefin foams is that they are generally not suitable for use where they would be exposed to a high service temperature environment, such as in proximity to an internal combustion engine or another source of heat and noise, due to a low heat distortion temperature. While some polymer foam materials have been developed to provide cushion properties that are capable of use in a relatively higher service temperature, they are either not suitable for efficient sound absorption over a wide range of frequencies or absorb water due to an open cell structure.
Therefore, there is still a need for improved thermoplastic polymer foam materials capable of meeting these criteria for use in such environments.
One aspect of the present invention is cellular thermoplastic polymer foams having an average cell size of at least 1.5 millimeter (mm), a density not greater than 300 kilograms per cubic meter (kg/m3), an average sound absorption coefficient of at least 0.2, and a heat distortion temperature of at least 110 degrees Celsius (xc2x0 C.), wherein the thermoplastic polymer comprises:
(A) at least one predominantly isotactic, propylene polymer having at least one of (1) a tan xcex4 value not greater than 1.5, (2) a melt tension of at least 7 centiNewtons (cN), and/or (3) a melt strength of at least 10 centiNewtons (cN) and optionally
(B) at least one ethylene polymer produced via a free radical process blended with the polypropylene polymer (A),
wherein:
the thermoplastic polymer comprises ethylene polymer (B) blended with the propylene polymer (A) in a weight ratio of not greater than about 65:35;
the thermoplastic polymer foam has at least one surface, the at least one surface having defined therein a multiplicity of perforation channels extending from the at least one surface into the foam such that there is an average of at least one perforation channel per 10 square centimeters (cm2) area of the at least one surface; and/or
the thermoplastic polymer foam has a density less than 25 kg/m3.
Another aspect of the present invention relates to a process for making polymer foams useful for sound absorption in an elevated temperature and/or moist environment comprising converting a foamable composition comprising at least one blowing agent and at least one thermoplastic polymer into a cellular polymer foam having an average cell size of at least 1.5 mm, a density not greater than 300 kg/m3, and at least one surface, the thermoplastic polymer comprising:
(A) at least one predominantly isotactic, propylene polymer having at least one of (1) a tan xcex4 value not greater than 1.5, (2) a melt tension of at least 7 centiNewtons (cN), and/or (3) a melt strength of at least 10 centiNewtons (cN) and optionally
(B) at least one ethylene polymer produced via a free radical process blended with the propylene polymer,
comprising at least one of the following three additional conditions:
selecting as the thermoplastic polymer a polymer blend comprising ethylene polymer blended with the propylene polymer such that the weight ratio of the propylene polymer (A) to the ethylene polymer (B) is at least 35:65;
perforating at least one surface of the cellular polymer foam product to introduce a multiplicity of perforation channels extending from the at least one surface into the foam such that there is an average of at least one perforation channel per 10 square centimeters of the at least one surface and/or converting the foamable composition into the cellular polymer foam such that the cellular polymer foam has a density less than 25 kg/3.
Another aspect of the process invention is a process for making polymer foams comprising:
(A) providing a cellular thermoplastic polymer foam having an average cell size of at least 1.5 mm, a density not greater than 300 kg/m3, an average sound absorption coefficient of at least 0.2, a heat distortion temperature of at least 110 degrees Celsius, and at least one surface wherein the thermoplastic polymer comprises:
(1) at least one predominantly isotactic, propylene polymer having at least one of a tan xcex4 value not greater than 1.5, a melt tension of at least 7 centiNewtons (cN) and/or a melt strength of at least 10 centiNewtons (cN) and optionally
(2) at least one ethylene polymer produced via a free radical process blended with the propylene polymer, and
(B) perforating the at least one surface of the polymer foam of step (A) so as to form a multiplicity of perforation channels extending from the at least one surface into the foam such that there is an average of at least one perforation channel per 10 square centimeters (cm2) area of the at least one surface.
Other aspects of the present invention include polymer foams obtainable, or preferably made, according to one or more of the above processes of this invention, which preferably have an average sound absorption coefficient of at least 0.2 and a heat distortion temperature of at least 110 degrees Celsius, and the use of the above foams to absorb sound, especially in a moist and/or elevated temperature environment.